1. Field of the Invention:
This invention relates to an audio apparatus which handles digital audio signals reproduced from compact discs, digital audio tapes, and the like, and more particularly relates to a sound field reproducing apparatus for reproducing in an ordinary room a sound field equivalent to that of a concert hall or the like.
2. Description of the Prior Art:
Recently, sound field reproduction has been attracting attention in the audio entertainment field. Sound field reproducing apparatus for recreating the sound field of concert halls and the like in an ordinary room have been developed. A conventional sound field reproducing apparatus comprises: a signal input unit for receiving digital audio signals reproduced from compact discs and the like; a signal processing unit for processing the input signals by performing time delay and feedback operations on them according to a specified procedure; a processing instruction unit for instructing the signal processor how to process the input signals; a system controller for modifying the signal processing instructions; and a signal output unit for outputting the digital signals from the signal processing unit.
The operation of the conventional sound field reproducing apparatus configured as mentioned above will be described below. The signals received by the signal input unit are processed by the signal processing unit according to the instructions indicated by the processing instruction unit, and converted to signals which are suitable for a certain sound field. Then, the outputs from the signal processing unit are supplied to an external digital-analog converter through the signal output unit so that they are converted to analog signals. Then these analog signals are audibly reproduced with a plurality of power amplifiers and loud speakers to reproduce, a desired sound field. For example, when the input signal is an impulse signal shown by (a) in FIG. 14, it is possible for the signal processing unit to make a plurality of impulse trains such as (b), (c), (d) and (e) of FIG. 14 of the signal to be input in each loud speaker, by performing time delay and adding operations. These impulse trains may be representative of initial reflected sounds of a certain sound field.
There are other types of sound field reproducing apparatus which can vary the state of a sound field to be reproduced. Such an apparatus for modifying a sound field generally comprises: a digital audio signal input unit; a signal processing unit for processing the digital input signals in a certain way to attain the sound field characteristics to be reproduced; a processing procedure memory for storing the processing procedures according to which the signal processing unit processes the input signals; a system controller for modifying the processing procedure sent from the processing procedure memory to the signal processing unit and for providing overall controls of the system operation; and a signal output unit for outputting the digital signals.
In such a conventional apparatus for changing a sound field, the digital signals received by the signal input unit are processed by the signal processing unit according to the processing procedure sent from the processing procedure memory. Then, the outputs of the signal processing unit are passed through the signal output unit, and converted to analog signals by an external D/A converter. These analog signals are then connected with amplifiers and speakers and the like so that they are rendered audible in a target sound field. When the characteristics of the sound field to be reproduced are to be changed, control codes are sent from the system controller to the processing procedure memory to change the processing procedure. Upon reception of the codes, the processing procedure memory transfers associated sound field data to the signal processing unit. The subsequent operation same as described above is conducted to change the reproduced sound field.
These conventional apparatuses for changing a sound field are problematical in that, when a processing procedure is changed for continuous shifting of the state of a reproduced sound field, a noise occurs in the output signals at a change from one procedure to another. This noise is attributable to the discontinuity of signals, etc. To prevent this problem from arising, the signals are cut off at a point of occurrence of the noise. Therefore, it has been impossible to change the sound field continuously without producing a break in signal output.